This invention relates generally to silicon solar cells, and more particularly the invention relates to a solar cell having improved anti-reflective surface passivation.
The silicon solar cell generates electrical charge when exposed to solar radiation. The radiation interacts with atoms of the silicon and forms electrons and holes which migrate to p- and n-doped regions in the silicon body and create voltage differentials between doped regions.
Typically, the silicon body is coated with a silicon dioxide passivation layer. This layer may also serve as an anti-reflection layer to impinging radiation, or, alternatively, an additional anti-reflection coating can be applied over the passivation layer. Heretofore, a problem with oxide passivation layers has been a degradation of the surface recombination velocity at the silicon-silicon dioxide interface when exposed to concentrated sunlight. This effect is primarily due to hot electrons being created by the ultraviolet end of the solar spectrum and being injected from the silicon layer into the silicon dioxide layer.
U.S. Pat. No. 5,030,295 to Swanson, et al. discloses a stable passivation for silicon solar cells in which a thin silicon dioxide layer is capped by a thin polysilicon layer. Without the presence of the polysilicon, the surface is damaged by the ultraviolet portion of the solar spectrum, resulting in degradation of cell performance with time. The polysilicon is hypothesized to prevent such damage by virtue of either its absorption of the ultraviolet light or its prevention of water vapor diffusing through the thin silicon dioxide layer. Water is known to reduce the radiation hardness of silicon dioxide passivation.
The present invention is directed to a similar silicon solar cell which has an improved anti-reflection passivation layer and to a method of fabricating the passivation layer.